Retention of Cs–Cl bond induces coordination polymer formation over trinuclear chiral assembly of copper(ii) complexes of l-leucine derived ligand

Abstract

The use of caesium is a less trodden path in terms of the synthesis of coordination polymers. The chemical similarity and mild toxic nature of caesium salts does not provide much impetus to work with these compounds compared to their potassium analogues. However, are the potassium and caesium salts really close in terms of coordination polymer formation? The result presented in this manuscript shows that while neither potassium halides or potassium nitrate inhibit the formation of a trinuclear chiral assembly of a copper(II) complex from a mononuclear Cu(II) complex, caesium chloride preferentially forms a coordination polymer while keeping the Cs–Cl bond intact. Under the same conditions, caesium nitrate does not inhibit the assembly formation. Structural characterization of {[CsCl{Cu(HL^L-leu)₂}(H₂O)]}_n (2) showed it to be a two-dimensional coordination polymer in the ab plane, where penta-coordinated Cu(HL^L-leu)₂ complex units (HL^L-leu = reduced Schiff base of L-leucine and the salicylaldehyde condensation product) were interconnected through the formation of Cu–Cl–Cs bonds. Multitudes of intermolecular H-bonds were observed as well. The use of KCl, KBr, KI or CsNO₃ in lieu of CsCl to the [Cu(HL^L-leu)₂(CH₃CN)] (1) facilitated the formation of the trinuclear assembly, [M{Cu(HL^L-leu)₂}₃]X, where M = K⁺ or Cs⁺ and X = Cl, Br, I or NO₃ depending on the salt used. The Cu(HL^L-leu)₂ units in these assemblies are hexacoordinated Cu(II) complexes.